Figures

- Constraints on nebular dynamics and chemistry based on observations of annealed magnesium silicate grains in comets and in disks surrounding Herbig Ae/Be stars

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Fig. 1. UV spectra obtained with the IUE of the Herbig Be star HD 100546 at two epochs (thin and thick lines). The spectra illustrate variability in the red-shifted infall features and variability in the strength of blue-shifted absorption associated with the stellar wind. The wind can be traced to 200 km/s. The electronic transitions involved are the Si+ UV multiplet 2 and the resonance doublet of C+3.

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Fig. 2. Three IR spectra (Upper) of amorphous Mg silicate smoke annealed in the laboratory for 6, 48, and 196 h at 1,027 K, fit by using seven gausian peaks and compared with the spectrum of dust in comet Halley, fit by using five of these same peaks.

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Fig. 3. Schematic drawing of a protostellar nebula (distance on a log scale) centered on the protoSun. The region of dust processing is shown (5 AU), infalling envelope, bipolar outflow, and less collimated wind. Comet formation is expected to occur from 5 to beyond 40 AU.